The present invention relates to a process for producing copper phthalocyanines which are important as organic pigments.
More particularly, it relates to a process for producing copper phthalocyanines having high quality and high tinting strength, without producing a toxic by-product by an advantageous industrial operation, which comprises reacting a phthalic anhydride or a phthalimide with a copper compound and urea in the presence of a catalyst in a specific polyalkyl monochlorobenzene.
It has been known that in the conventional industrial process for producing the copper phthalocyanines by reacting a phthalic anhydride or a phthalimide with a copper compound and urea in the presence of a catalyst, the yield of the copper phthalocyanine is highly affected depending upon the selected reaction solvent, and also the tinting strength and the hue are highly affected depending upon the selected reaction solvent. It has been also known that in the physical properties of the optimum reaction solvent, the boiling point at the atmospheric pressure should be in a range of 160.degree. to 250.degree. C. and the difference between the initial boiling point and the dry point should be less than 10.degree. C. and the thermal stability should be high.
Usually, trichlorobenzene, nitrobenzene and alkylbenzenes have been used as the reaction solvent having the optimum physical properties.
However, trichlorobenzene has high toxicity and reacts via the Ullmann reaction to form polybiphenylchloride (PCB) which is toxic and is a common and severely disturbing pollution source by polycondensation of trichlorobenzene, because the copper compound is included in the reaction system.
Nitrobenzene is also toxic so that the allowable concentration in air is regulated to be less than 1 ppm from the viewpoint of the labor hygiene. When nitrobenzene comes into contact with the skin, it is rapidly absorbed into the skin. When nitrobenzene is used in industrial operations, it is necessary to equip an expensive apparatus for collecting it to prevent the discharge in order to maintain the allowable concentration. Accordingly, nitrobenzene is not suitable as the reaction solvent in industrial operations.
Alkylbenzenes have the wide range of the boiling point and accordingly, when alkylbenzenes are recovered by distillation under a reduced pressure after the reaction, an amount of a residue having high boiling point is large to cause low recovery ratio and the operation is complicated disadvantageously. When the residue is included in the copper phthalocyanines, the tinting strength in the pigmentation is inferior and the hue is inferior.